This invention relates to dielectric resonator apparatus having a plurality of dielectric resonators formed inside a dielectric block. This invention also relates to dielectric resonator apparatus having a plurality of such dielectric resonators formed unistructurally.
It has been known, as an example of prior art apparatus of this kind, to provide a plurality of inner electrodes serving as resonant conductors inside a dielectric block of a rectangular parallelopiped and an outer conductor on its outer surfaces to thereby produce a dielectric resonator apparatus having multi-stage resonators. Such unistructurally formed dielectric resonator apparatus are convenient because they do not require a shielding case or brackets for attaching to a circuit board and can be surface-mounted easily.
For producing dielectric resonator apparatus having different numbers of resonators in a dielectric block, however, it was necessary to provide many different kinds of molds. In other words, many molds had to be prepared for producing dielectric resonator apparatus with various characteristics and this affected their production costs adversely. Moreover, since the distances between the resonators are determined by the dimensions and the shapes of the molds, it was difficult to accurately set the degree of coupling between the resonators. In the case of a prior art combine-type dielectric resonator apparatus, for example, the setting or adjustment of the degree of coupling between the resonators was intimately related to that of the resonance frequencies of the individual resonators such that a change in one would affect the other and hence that it was difficult to set or adjust both of them independently. Since a plurality of mutually parallel inner conductors are arranged inside a single dielectric block, furthermore, the external dimension of the dielectric block will increase in the direction in which these inner conductors are arranged as the number of stages is increased. This reduces the degree of freedom in making connections to connector terminals when it is mounted to a circuit board.